Related Stories

US researchers have developed a prenatal blood test that they believe can be used to determine if an unborn baby has Down syndrome without the need for invasive testing methods such as amniocentesis.

Researchers led by Professor Stephen Quake of Stanford University in California have created a way to look for the extra chromosomes that cause Down and similar birth defects in the tiny amounts of foetal DNA that circulate in the mother's blood.

The test, which requires a small blood sample from the mother, is safer than amniocentesis, in which a needle is stuck into the uterus, and can be done earlier in a pregnancy.

Down syndrome, which causes mental retardation and other problems, is caused when a child has three copies instead of the normal two of chromosome 21.

The test also detects other chromosomal conditions such as Edward syndrome, which kills half of babies in the first week of life and Patau syndrome, which kills more than 80% of children in infancy.

Non-invasive

Quake's team demonstrated the accuracy of the new genetic test in a small study involving 18 women.

It accurately identified the nine women with a Down syndrome pregnancy and three others with foetuses with different chromosomal disorders, the researchers write.

"It's the first universal, non-invasive test for Down syndrome. So this should be the first step in putting an end to invasive testing procedures like amniocentesis and chorionic villus sampling," says Quake.

Blood tests for pregnant women like the alpha-fetoprotein test can find potential signs of a chromosomal disorder such as Down syndrome, but cannot diagnose it with certainty.

Quake says such tests serve as only "indirect and weak predictors of what's going on."

For a definitive determination, women must have an invasive diagnostic procedure such as amniocentesis or chorionic villus sampling (CVS). This is done typically after the 15th week of pregnancy.

These procedures carry a small risk - roughly 1% - of causing a miscarriage or birth defects.

Because of that, their routine use has been mostly by women age 35 years and older, who are at higher risk for having Down syndrome babies.

Quicker results

Quake says the new test also could be administered much earlier in a pregnancy than amniocentesis or CVS - potentially as early as five weeks after conception. And the results are back within a couple of days, instead of two to three weeks.

He says the new test could be widely available in two or three years, and could become a routine prenatal test of a baby's health.

The next step is a larger study involving hundreds of women, says Quake.

Stanford University has filed a patent on the test and two companies are negotiating for the licensing rights, he says.

Quake has been hired as a consultant for both companies, which he declined to identify.